DESCRIPTION: (Adapted from applicant's proposal.) This Core participates in the design of experiments and interpretation of results, coordinates animal studies, houses animals to prevent intercurrent disease, and monitors animal health. All rats will be obtained through the NIA, and maintained under isolation conditions to prevent intercurrent infectious diseases. The Core utilizes established programs in laboratory animal medicine and pathology to assess the disease status of the rats. This is considered critical for distinguishing between age effects and disease processes resulting from infection or environmental factors.